After holes have been drilled in the "roof" of a subterranean gallery, a bolt is inserted in each hole. The bolt comprises a a bolt comprising a socket at its end, which, by to an expansion effect, is anchored in the bottom of this hole, after which tightening of this bolt brings about compression of the earth in the form of a column concentric with the shank of said bolt. The recent development of this method has seen expansion bolts replaced by rods sealed with resin, but three essential operations, namely: drilling of the hole, insertion of the bolt and tightening of the bolt, always have to be carried out.
French Pat. No. 1,359,297 discloses an apparatus which on its own and without having to be moved, is capable of carrying out these three operations in succession, by simple pivoting of the apparatus about the axis of a rod anchored in the "roof" of the level. This drilling and bolting apparatus essentially comprises a girder of H or other section, on which two carriages may slide, one for the drilling of the hole and the other for the introduction of the bolt into this hole and its tightening. The girder is able to pivot about the axis of the anchoring rod so that after pivoting, the axis of the bolt is aligned with the axis of the hole drilled immediately before the operation for introducing the bolt.
One difficulty encountered in the use of this apparatus is in making the axis of the bolt coincide exactly with the axis of the hole drilled previously, the diameter of the hole being only slightly greater than that of the bolt. This difficulty is all the greater, the greater the height of the gallery and its causes are varied. For example, the anchoring point may have undergone a slight shift or the design of the apparatus which comprises numerous parts able to move with respect to each other, as well as wear, causes inevitable play. Consequently, the introduction of the bolt must frequently be carried out, in practice, by a man standing on a mining car, thus defeating the initial purpose of the apparatus which is to eliminate any manual intervention.
To resolve this difficulty, and facilitate the introduction of the bolt (or resin cartridges), the aforesaid apparatus has been improved, according to the Certificate of Addition No. 2 337 250 of the above mentioned French Patent Specification, by providing that, at its upper end, the girder of H section supports a reaming device which is coaxial with the drilling bit, coming into operation at the end of the drilling operation, before pivoting of the girder, in order to widen the mouth of the hole drilled in the form of a cone. The reaming device comprises a reamer surrounding the drilling bit, the reamer being free to rotate and move longitudinally with respect to the bit, but being able to be set in rotation and to be pushed forward at the same time as the bit, when the drilling carriage virtually reaches the end of its travel. This arrangement makes it possible to dispense with an additional motor for driving the reamer and it makes it possible to set the reaming device in operation automatically when the drilling carriage virtually reaches the end of its travel. However, it has two features requiring improvement.
Firstly, in order to drive the reamer when the bit arrives close to its end of travel position, it is necessary to provide coupling means between the rotary support for the bit and the reamer. These means, constructed in the manner of a clutch, either a friction clutch or other type of clutch, complicate the construction so that the advantage of eliminating an additional motor is illusive.
Secondly, in view of the fact that the reamer comes into operation solely when the hole has been virtually completely drilled by the bit, the collection of dust during drilling is unsatisfactory, even if a container for collecting the dust has already been provided for this purpose on the apparatus.